Low-running-temperature tyre

ABSTRACT

A tyre for a wheel of a vehicle comprises a toroidal carcass provided with axially opposite sidewalls and beads for anchoring the tyre to a rim of the wheel, a tread band located crownwise on the carcass, comprising a surface with a plurality of hollows and grooves defining a raised tread pattern, and a belt structure interposed between the carcass and the tread band, axially extending between the sidewalls. The tread band comprises at least first and second circumferential axially-contiguous portions arranged to contact a road surface. The first portion is formed of a first composition comprising a reinforcing filler having at least  40 %-by-weight carbon black and at least some white filler, the second portion is formed of a second composition comprising a reinforcing filler having at least  20 %-by-weight white filler, and the first composition is different from the second composition. A difference of compositions between the at least first and second portions achieves a tyre operating temperature lower than a reference temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/738,132, filed Dec. 18, 2003, which is a continuation of U.S. patentapplication Ser. No. 09/802,948, filed Mar. 12, 2001 (now abandoned),which is a continuation of U.S. patent application Ser. No. 09/472,019,filed Dec. 27, 1999 (now abandoned), which is a continuation of U.S.patent application Ser. No. 09/041,951, filed Mar. 13, 1998 (nowabandoned); further, Applicants claim the right of priority under 35U.S.C. § 119(a)-(d) based on patent application No. MI97A 000584, filedMar. 14, 1997, in the Italian Patent Office; the contents of all ofwhich are relied upon and incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tyres for mounting on vehicle wheels,and more particularly to tyres for motorcycles and cars, but it may alsorelate to any other type of tyres. More specifically, the inventionpertains to the tread band used in tyres, which also includes raw orpre-molded treads for covering or “recapping” worn tyres, as well as toa method of achieving optimal thermal conditions during use of the tyre.

2. Description of the Related Art

It is known that today tyres must not only possess good performancefeatures in terms of operating on any kind of road surfaces, i.e., dry,wet, or snow-covered surfaces, but also must have good qualities such asa comfortable and smooth ride and high mileage. These features must bemaintained even when the tyre runs under critical or extreme conditions,due for example to high speed operation in connection with racing on atrack, in particular in combination with a high ambient temperature.

These performance and operational features of the tyre are determined bygrooves and circumferential and/or transverse hollows of appropriatesizes and orientation that are formed in the tread band. These elementsgive rise to ribs and/or blocks variously located in the tread band soas to form different designs of tread pattern, optimized according tothe intended use for the tyre. In particular, said pattern can bedefined as symmetric when it is always the same irrespective of therolling direction of the tyre, asymmetric when one side of the treadband is different from the axially opposite side, and finally,directional when the tyre is designed to operate in a preferred rollingdirection. In the last case, one side of the tread band is a mirrorimage of the other side, relative to the equatorial plane of the tyre.

Preferably, in particular for the purpose of obtaining good traction onwet or snow-covered road surfaces and on curvy roads, blocks and ribsare provided on the tread band to form an appropriate pattern. Thispattern includes a series of narrow grooves of greater or lesser densityor width, oriented in a direction substantially perpendicular to thedirection of vehicle movement along which traction has to be provided.

It is known that the performance of the tyre is adversely affected to agreat extent by the operating temperature of the tyre. One of the mostdifficult problems to be solved has always been and still is that ofmaintaining a good resistance to wear and appropriate grip at normaltemperatures of operation of the tyre (30° C.-50° C.), as well as whenthe tyre exceeds those temperatures due to strong thermal and mechanicalstresses, such as those resulting from use under so-called “extremeconditions.”

The difficulty in obtaining these desired features of the tyre under alloperating condition essentially originates from the fact that resistanceto wear and appropriate grip are two goals substantially incompatiblewith each other. For the tyre to achieve a good resistance to wear andlow resistance to rolling, elastomeric blends having a low hysteresisvalue must be employed in forming the tyre tread band. However, theseblends are capable of dissipating a limited amount of energy duringrolling.

On the other hand, to achieve the desired tyre grip or traction,elastomeric blends of a high hysteresis value are required. These blendsare capable of dissipating an amount of energy sufficient to ensureproper adhesion between the tread band and the ground.

It is important to remember that the temperature reached by theelastomeric blend in operation is proportional to the amount ofdissipated energy, and therefore to its hysteresis value. As a result,an optimal elastomeric compound forming the tread band should have quiteopposite hysteresis behaviors, incompatible with each other, tosimultaneously optimize all desired performance features of the tyre.

So far, attempts carried out in the art to improve tyre performance in atemperature range different from the temperatures of normal use haveresulted in either a large and undesired loss of grip, or in asignificant worsening in the resistance to abrasion of the tread band.In some cases, both drawbacks were present.

Pirelli in the past has also tried to solve this problem, in particularwith a tyre being the object of Italian Patent No. 1,087,461 to itsname. The tyre described in that patent is provided with a tread bandconsisting of two axially contiguous circumferential portions ofdifferent composition, the first portion of which is made of anelastomeric blend having a low glass-transition temperature (referred toas “Tg”), included between −55° C. and −30° C., whereas the blend of thesecond portion has a higher Tg, included between −25° C. and −10° C.Although some advantages were achieved under conditions of normal orhigh operating temperatures, under winter conditions when the tyre issubject to low environmental temperatures close to the temperature ofthe highest Tg (−10° C.), the tyre showed a significant decay in itsoperational performance.

In view of the above, the described problem appears to be substantiallyunsolved by the known art. In particular, tyre tread bands of known typecannot maintain the same grip when the tyre, under extreme useconditions, exceeds the above mentioned standard temperatures of use(30°-50° C.), without, on the other hand, simultaneously losing theirresistance to abrasion.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, it has been unexpectedly foundthat it is possible to retain the tyre performance existing under normalconditions, while improving such performance to a higher level duringtyre use under extreme conditions.

Applicants approached the problem of producing tyres with tread bands ofdifferent material while developing a tyre having coloured inserts, suchas for example a white sidewall, and in particular tyres with a treadband of two distinct colours. A two-coloured tyre, in addition to havingan agreeable and unusual aesthetic aspect which enables carpersonalization by an owner with his/her preferred colours, may alsohave more practical functions such as enabling a correct mountingorientation of the tyre on the vehicle when required, or an immediateidentification of the type of tyre stored among a great number of othertypes in a warehouse that may be poorly illuminated.

Applicants realized that making coloured elastomeric blends excludes theuse, even in minimum proportions, of carbon black as a reinforcingfiller, because carbon black has such a colouring power that the effectof any other coloured pigment is drowned out.

Only so-called “white” fillers can be coloured with appropriatepigments. Among these, the preferred fillers for use in tyres,especially in the tread band region, have been identified as fillers ofsiliceous material, in particular silica.

It is known that silica is useful for giving the tyre qualities of lowrolling resistance, due to the low hysteresis value of the silica filledelastomeric blend, and good grip on snow-covered or wet ground. Silica,however, offers lower performance regarding grip on a dry ground andresistance to wear, so that its use as a reinforcing filler in the tyretread band must be carefully controlled.

Applicants observed the results of road tests of a series of prototypeshaving the tread band consisting of two different circumferentialportions located axially side-by-side, one portion consisting of anelastomeric blend mainly filled with carbon black (black blend) and theother consisting of a blend exclusively filled with white filler (whiteblend). Applicants ascertained that the performance on a dry road ofthose tyre prototypes were always globally better than those of thegroups of control tyres, having respectively the tread band made of ablend filled with carbon black, or with a very high percentage ofsilica.

While conducting studies to clarify the reasons of these unexpectedresults, Applicants carried out some thermographies of the tread band oftyres being tested, thus finding out that the two-coloured tyresaccording to the invention tended to operate at a lower temperature thanthe black tread tyres. In particular, even the black tread portion ofthose prototypes operated at a lower temperature than the equivalenttread portion in the tyres with a completely black blend tread band.

The improvement achieved in accordance with the present invention in theroad behavior of two-coloured tyres, as compared with conventionaltyres, is believed to result from the lower operating temperature of thetyre. The improvement achieved relative to white tyres depends on theabove mentioned and known deficiencies typical of silica filledelastomeric compounds in connection with important aspects of the tyreperformance on the road.

In particular, the white blend portion, or in any case the portionformed of a low-hysteresis blend that is a “cold” operating blend, intyres provided with a two-blend tread band is deemed to generate asynergetic action linked to its lower operating temperature. Thissynergy tends to keep the adjacent tread band portion formed of a blackblend colder than in a conventional design, in addition to keeping theoverall tread band colder.

The invention is considered capable of carrying out its effects in aperceptible manner when differences between the hysteresis values and/orthe white filler amounts in the two elastomeric blends used in the treadband are preferably included within given limits, as more specificallydescribed below.

In accordance with a first aspect of the present invention, a method hasbeen found of controlling the working temperature of a tyre comprising atoroidal carcass provided with axially opposite sidewalls and beads foranchoring to a corresponding mounting rim, a tread band locatedcircumferentially on the crown portion of said carcass and molded with araised pattern for rolling contact with the ground, and a belt structureinterposed between said carcass and tread band, axially extending in acontinuous manner between said sidewalls. The method consists in makingthe tread band of at least two circumferential and axially contiguousportions, a first portion and a second portion respectively of differentcompositions, which compositions have a different hysteresis value. Thedifference between said two hysteresis values results in a workingtemperature of the tyre which is lower, as a whole, than the temperatureof a conventional tyre with a tread band made of the composition havingthe greater hysteresis value.

It has been found that preferably the difference between said hysteresisvalues must be at least equal to 10% of the higher value, and preferablygreater than 20% of said higher value.

In accordance with a different aspect of the invention, it has beenfound that an alternative method may be carried out by making the tyretread band of two circumferential portions, located axially inside-by-side relationship, from different compositions. The compositionsare respectively a white one and a black one. At least one of thecompositions comprises a white filler as the reinforcing filler. Thedifference between the amount of white filler present in each of the twocompositions is selected to obtain an operating temperature of the tyrewhich, as a whole, is lower than the operating temperature of a tyrehaving a tread band made only of the composition containing the loweramount of white filler.

It has been found that the so-called black composition must preferablycontain at least 40%-by-weight of carbon black, whereas the so-calledwhite composition must contain at least 20%-by-weight of white filler,relative to the total amount of reinforcing filler. More specifically,the white blend must contain an amount of white filler, in terms offiller weight, greater than the amount contained in the black blend. Thefiller amount difference between the two blends must preferablycorrespond to a percent difference of at least 20% between thepercentages-by-weight of white filler out of a total amount of thereinforcing filler in each of the two blends.

In a different aspect the invention relates to a tyre for vehicle wheelscomprising a toroidal carcass provided with axially opposite sidewallsand beads for anchoring of said tyre to a corresponding mounting rim, atread band placed crownwise to said carcass. The tread band comprises aplurality of hollows and grooves variously located relative to theequatorial plane of the tyre, adapted to define a raised tread patternfor rolling contact with the ground. A belt structure is interposedbetween said carcass and tread band, axially extending in a continuousmanner between said sidewalls. The tread band is formed of at least twocircumferential and axially contiguous portions, a first portion and asecond portion respectively, formed of different compositions ofelastomeric compounds, characterized in that said compositions havedifferent hysteresis values. The difference between said two hysteresisvalues is selected to obtain a working temperature in the tyre which islower, as a whole, than the working temperature of a tyre having a treadband made only of the composition showing the greater hysteresis value.

In a further aspect, the invention relates to a tyre for vehicle wheelscomprising a toroidal carcass provided with axially opposite sidewallsand beads for anchoring the tyre to a corresponding mounting rim, atread band located crownwise to said carcass comprising a plurality ofhollows and grooves variously located relative to the equatorial plane,adapted to define a raised tread pattern for rolling contact with theground, and a belt structure interposed between said carcass and treadband, axially extending in a continuous manner between said sidewalls.The tread band is formed of at least two circumferential and axiallycontiguous portions, a first portion and a second portion respectively,formed of different compositions. The first portion comprises areinforcing filler of carbon black including at least 40%-by-weight ofsaid carbon black, and the second portion comprises a white reinforcingfiller in an amount at least equal to 20%-by-weight of the total amountof reinforcing filler in the elastomeric composition of the secondportion. The composition difference between the two portions is selectedto obtain a working temperature in the tyre that, taken as a whole, islower than the temperature of operation reached by a tyre with a treadband made only of the composition containing the lower amount of whitefiller.

It has been found preferable for the second portion to contain thegreater amount of white filler, and for the difference between theamounts of said white filler present in the compositions of the twoportions to be at least equal to 20%-by-weight in favor of the second or“white” portion, provided that the volume of white filler in said secondportion is such that the decrease in operating temperature describedabove is obtained.

In accordance with the invention, it has been found preferable for thevolume of said second portion to be at least as high as 30% but nothigher than 80% of the overall volume of the tread band. In a furtherdifferent aspect of the invention it has been found preferable for theaxial width of said second portion to be at least as high as 25% but nothigher than 80% of the overall width of the tread band, and preferablygreater than 50%.

In a further novel and still different aspect, the invention is a treadband that can be made of raw blend or of an already pre-molded blend,for use in covering or “recapping” worn tyres. The tread band can thenbe made according to any one of the above mentioned differentalternative embodiments.

In another and still different aspect, the invention also relates to amethod of producing tyres for vehicle wheels, and specifically treadbands for said tyres having coloured inserts of colours different fromblack.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is an axial transverse section of a tyre of the type used infour-wheeled vehicles, in accordance with one embodiment of theinvention;

FIG. 2 is an axial transverse section of a tyre of the type used intwo-wheeled vehicles, in accordance with another embodiment of theinvention;

FIG. 3 is a plan view of a portion of tread band in accordance with theinvention, showing a tread pattern of the symmetric type;

FIG. 4 is a front view of a tyre with a tread band in accordance withthe invention, showing a tread pattern of the asymmetric type;

FIG. 5 is a plan view of a portion of tread band in accordance with theinvention showing a tread pattern of the directional type; and

FIG. 6 is a colour thermograph of a tyre tread in accordance with theinvention compared with that of tyre of known type, referred to the sametread pattern, of the asymmetric type, under the same workingconditions.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows the structure of the inventive tyre in an embodiment usedin four-wheeled vehicles. Such structure other than the tread band doesnot differ substantially from the general structure of traditionaltyres, however the differences with the latter will become apparent inthe following description.

Tyre 1 comprises a carcass 2 of a strong structure formed of at leastone ply 3 of rubberized fabric comprising reinforcing cords of textileor metal material buried into the elastomer material of the fabric, saidply having its ends 3 a each turned up about an anchoring ring or bead4. The bead core is provided on its radially outer surface with a rubberfilling 5. Preferably the turned-up flaps 3 a of the carcass pliesextend up radially outwardly along at least part of the side of saidfilling.

As known, the tyre area comprising bead core 4 and filling 5, that isthe radially inner portion of the tyre sidewall, forms the tyre beadwhich is intended for anchoring of the tyre to a corresponding mountingrim.

Located in known manner on the carcass, which is preferably of theradial type having the reinforcing cords lying in planes along the tyreaxis of rotation, there is a tread band 10, provided with a raisedpattern intended for rolling contact of the tyre on the ground. Thewidth L of this band is identified by the distance between theintersection points of the tread band and sidewall curvatures, referredto as the edges of the tread band.

This tread pattern may be comprised of a plurality of ribs and/or blocks11, 12 separated from each other by corresponding hollows and grooves13, 14, directed both circumferentially and transversely. Said ribsand/or blocks may be provided with various cuts and narrow slits or“lamellae” 15, forming configurations well known to those skilled in theart.

Tyre 1 may also be comprised of a belt structure 6 located crownwise oncarcass 2, interposed between the carcass and tread band, extending fromone side to the other side of the tyre, i.e., substantially as wide asthe tread band, and comprising two radially superposed layers 7, 8 ofreinforcing cords. The reinforcing cords are preferably of metalmaterial and are parallel to each other in each layer, but are locatedin crossed relationship with those cords of the adjacent layer relativeto the equatorial plane of the tyre. In a preferred embodiment, afurther radially outermost layer 9 of reinforcing cords, preferably oftextile material, and more preferably of a heat-shrinkable material(nylon) oriented at 0° relative to a circumferential direction, islocated between the tread band and the radially more internal beltlayers.

In accordance with the invention, the tread band is formed of twocircumferential portions, a first (hot) portion A and a second (cold)portion B respectively, which are axially contiguous and made up ofdifferent compositions. More specifically, said two compositions have adifferent hysteresis value, and the difference between the two values issuch that it causes each portion, during the tyre operation, to operateat a different temperature. Preferably, the hysteresis difference mustbe at least equal to 10% of the higher hysteresis value, and morepreferably greater than 20% of said value.

The hysteresis value to which reference is made above is the loss factor(tan δ) measured on a cylindrical test piece of 14 mm diameter and 25 mmlength, tested under the following conditions: temperature of 70° C.,deformation frequency equal to 100 Hz in a sinusoidal condition, on a25%-precompressed test piece submitted to a further deformation width of3.5% relative to the size of the undeformed test piece.

It is preferable for the test piece to be submitted in known manner,before measurement, to a conditioning cycle in terms of time andfrequency cycles, so as to stabilize data of the subsequent measurement.Said test piece may be also obtained from several suitably-superposedslices of reduced thickness that, for example, can be removed from partsof the tyre tread.

In an alternative embodiment, the two circumferential portions comprisea first (black) portion A and a second (white) portion B. Morespecifically, said two portions are made of elastomeric compositionsthat have different reinforcing fillers, including a white filler. Thedifference between the amount of white filler present in the A and the Bportions is at least equal to 20% of the amount present in the whiteportion.

It has been found that preferably the black composition must contain atleast 40%-by-weight of carbon black, whereas the white composition mustcontain at least 20%-by-weight of white filler, measured relative to thetotal amount of the reinforcing filler in the respective elastomericcomposition mixtures. The two compositions have a difference in amountof white filler contained that is at least equal to 20%-by-weight, withthe white composition having more of the white filler.

It has been found that the invention accomplishes its goals in aparticularly appreciable manner when the volume of the second portion B,i.e., that of the cold or white composition, is such that the overalloperating temperature of the tyre is reduced relative to a referencetemperature. The reference temperature can be either the operatingtemperature of an equivalent tyre submitted to the same operatingconditions but provided with a tread made entirely of the coldcomposition having a greater hysteresis value or, alternatively, of anequivalent tyre provided with a tread made entirely of the blackcomposition having the smaller amount of white filler and lowerhysteresis value.

More specifically, it has been found that when the volume of said secondportion B represents a significant percentage of the overall volume ofthe tread band, the operating temperature of both the entire tread bandand of each separate blend portion, as well as of all the tyre taken asa whole, remains lower than the reference temperature of an equivalenttyre having the tread band made entirely of the black, or hot,elastomeric composition. By “equivalent tyre” it is herein intended atyre identical to the tyre according to the invention, except for thedifferent elastomeric composition forming the tread band.

It has been found that in a tyre formed according to the invention, thedecrease in the overall operating temperature of the tyre, i.e., theinner temperature of the tyre, is on the order of at least 5° C. ormore, relative to an equivalent tyre.

In accordance with the invention, a “significant percentage” of theoverall volume of the tread band is deemed to mean an amount at least ashigh as 30% of the overall volume of said tread band, and preferablyhigher than 50%. This percentage indicates how much of the tread band isformed by an elastomeric compound having the higher proportion of whitefiller. On the other hand, increasing this percentage reduces the treadresistance to wear and increases grip loss, so that in order to maintainthe good performance qualities achieved by the tyre of the invention,the volume of this second portion B of the tread band should not exceed80% of the overall volume of said tread band.

The ideal relative volume of the two tread band portions also depends onthe features of the pattern formed thereon, and in particular on theratio between lands and hollows. This ratio is generally differentbetween the two portions in the case of asymmetric patterns, so that thewidth of the second portion, i.e., the so-called cold or white portion,is preferably included between 25% and 80% of the overall width of thetread band, and more preferably greater than 50% of said width.

In another preferred embodiment of the invention designed to provide acoloured composition, in the second portion B the white filler ispreferably used in an exclusive manner as the reinforcing filler. Inother words, the second portion B preferably forms a coloured insertsubstantially devoid of carbon black. In accordance with the invention,this colouring of the second portion is preferably obtained by mixingthe white filler with colouring pigments selected from a wide variety ofpossible colours. Many suppliers can provide these colouring agents andcompositions containing an already coloured white filler. Applicantsselected the material available from the Italian associated firmCLARIANT to assemble a tyre according to the invention.

With reference to the blends used in the invention, it is to note thatcarbon black for the reinforcing filler is known in the art. Applicantspreferably use carbon black having an absorption value DBP measuredfollowing ISO 4656-1 standards equal to at least 100 ml/100 g,preferably included between 130 ml/100 g and 160 ml/100 g, and a surfacearea as determined based on cetyltrimethylammonium absorption accordingto ISO 6810 standards (CTAB) not exceeding 130 m²/g, and preferablyincluded between 70 m²/g and 115 m²/g.

The so-called “white” fillers, for example, are reinforcing fillers ofinorganic type such as gypsum, talc, kaolin, bentonite, titaniumdioxide, silicates of various kinds, and silica. Preferably the whiteblend of the invention comprises a silica-based white filler that is areinforcing agent based on silicon dioxide (silica), silicates, andmixtures thereof having a surface area measured according to BET methodfollowing ISO 5794-1 standard included between 70 m²/g and 300 m²/g, andan appropriate binding agent capable of chemically reacting with silicaand bonding silica with a polymeric base during vulcanization. Among thegreat number of available binders, Applicants have found it convenientto use a known silane binding agent, identified as Si69, available fromDEGUSSA.

With regard to the polymeric base of the blends in accordance with theinvention, it can be selected from the group comprising: natural rubber,1,4-cis polybutadiene, polychloroprene, 1,4-bis polyisoprene, optionallyhalogenated isobutene-isoprene copolymers, butadiene-acrylonitrile,styrene-butadiene copolymers and styrene-butadiene-isoprene terpolymers,obtained both in solution and in emulsion, and ethylene-propylene-dieneterpolymers. In accordance with the invention, these polymeric bases canbe used individually or in a mixture thereof in accordance with thefeatures that are wished to be imparted to the finished product.

By way of example only and not in a limiting sense, two examples ofcompositions are given hereinafter for the black blend and the whiteblend respectively, that may be used for tyres in accordance with theinvention.

The elastomeric composition of portion A, in the version with areinforcing filler exclusively of carbon black, may have the followingcomposition, set forth in parts-by-weight:

polymeric base 100.0 carbon black 68.0 ZnO 2.0 stearic acid 1.0antioxidants 2.5 anti-fatigue agents 1.0 plasticizers 15 sulphur 1.2accelerating agents 1.8

The elastomeric composition of portion B, in the version including onlysaid silica-based white filler as the reinforcing filler, may have thefollowing composition, set forth in parts-by-weight:

polymeric base 100 silica 70 binding agent 8% of silica ZnO 2 stearicacid 1 antioxidants 2.5 anti-fatigue agents 1 plasticizers 15 sulphur1.2 accelerating agents 2.5

For achievement of the results of the invention, said second portion Bmay be located either in the central area of the tread band, flanked onboth sides by portions A, as shown in FIG. 5, or at a side position onthe tread band, adjacent an edge of the tread band, as shown in FIG. 4.However, due to the fact that the second portion B is more sensitive towear and to grip loss than the first portion A, the most convenientposition for the second portion B, at least for tyres used in situationsthat are not extremely demanding, is near the inner edge of the treadband, nearest to the vehicle centerline when the tyre is mounted on thevehicle, where stress is lower during operation of the tyre. Inhigh-performance tyres or tyres used in extremely demanding conditions,the centre position will be the preferred one when symmetric anddirectional tread patterns are utilized, while the side position will bethe preferred one for asymmetric patterns. Actually, such asymmetrictread patterns also have two axially distinct circumferential areas withreference to mounting of the tyre on the vehicle, an inner area nearerthe vehicle centerline and an outer area further from the vehiclecenterline, respectively. In this case, said second portion B ispreferably situated at the inner area of the pattern, that is the onewhich is located nearer the vehicle centerline.

Use of a compound portion reinforced with a white filler, as alreadydescribed, also enables a convenient colouring of this portion. Asexplained, it is apparent that it may be difficult to visually mount atyre with a symmetric or directional tread pattern made only of blacktread band compound, so that the portion to be mounted on the vehicleside is in the correct orientation. It is therefore apparent that bydifferently colouring inserts corresponding to different tread portions,this mounting problem too can be solved.

The invention can also be advantageously applied to tyres formotorcycles. These tyres (FIG. 2) are distinguished by a high transversecurvature, identified by the value of the ratio of the distance ht ofthe tread centre from line b passing through the tread ends C-C,measured on the equatorial plane, to the distance wt between said treadends C-C. This value, generally greater than 0.15 in tyres for frontwheels, is often even greater than 0.30 as compared to an usual value intyres for cars on the order of 0.05. Throughout the present descriptionsaid ratio will be referred to as “curvature ratio.” In motorcycletyres, according to the present invention, the tread width must beinterpreted as a measurement of the tread extension along its curvatureprofile.

FIG. 2 generally shows a motorcycle tyre of this type, comprising a veryparticular geometry structure capable of withstanding very particularuse conditions. As is known, two-wheeled vehicles in covering acurvilinear trajectory lean toward the internal side of the turn by anangle referred to as “camber angle,” the value of which can reach 65°relative to a plane vertical to the ground.

In this motorcycle tyre, a carcass structure which is substantiallyidentical to that previously described is provided. The same referencenumerals as shown in FIG. 1 have been also used here. However, in thiscase the belt structure 6 comprises a reinforcing wrapping which is anessential element, and consists of at least a preferably metallicinextensible cord 9 reaching circumferentially crownwise to the carcassply 3 to form a plurality of turns 9 a parallel to each other andlocated consecutively in side-by-side relationship, substantiallyoriented along the rolling direction of the tyre 1. The radiallyunderlying layers 7,8 of inclined cords are optional.

Turns 9 a are located consecutively in side-by-side relationship along acurvilinear profile, and by virtue of their substantial longitudinalinextensibility, structurally and dimensionally stabilize tyre 1 tomaintain the desired transverse-curvature profile.

In accordance with the invention, the tread band 10 is convenientlyformed of said portions A and B made of different elastomeric compounds.The cold or white blend portion B is preferably located on either sideof the equatorial plane of the tyre for reasons of structural andoperating symmetry of the tyre, due to its particular geometric shapeand the operating conditions of the leaning vehicle in a turn. In otherrespects, the same considerations, restrictions, and critical valuesalready mentioned above are also valid for this type of tyre.

FIG. 3 shows a plan view of a portion of tread band for a tyre accordingto the invention, molded with a known tread pattern of the symmetrictype. With regard to these pattern types, disposition of the white blendportion B can take place in any desired manner, both at a side positionrelative to the tread band or at a centre position in a central area ofthe tread band. In a preferred embodiment shown in FIG. 3, portion B isshown in cross-hatching and is located at a central position, extendingaxially from the equatorial plane of the tyre. In connection withparticular technical requirements or for other reasons to be met, saidportion B can be located either on one or both of the shown band sides11, on either side of the equatorial plane, or can be divided into aplurality of circumferential areas alternating with black blend areas.

FIG. 4 is a front view of a tyre provided with a tread band inaccordance with the invention, molded with a tread pattern of theasymmetric type which has an inner circumferential area I locatedaxially in side-by-side relationship with another outer circumferentialarea E.

As described above, the tyre is mounted on the vehicle so that area I islocated near the vehicle centerline and area E is located further awayfrom the vehicle. With this asymmetric type, the white blend portion B(in cross-hatching) is preferably located in a side portion of the treadband and, most preferably, on the inner side area I.

FIG. 5 is a plan view of a portion of the tread band of a tyreembodiment according to the invention, molded with a tread pattern ofthe directional type. In this pattern, the white blend portion B (incross-hatching) will preferably be located in a central position and,most preferably, on either side of the equatorial plane of the tyre.

The performance of the tyre according to the invention has been analyzedunder operating conditions, with that of an equivalent black tyre takenas a reference, by adopting a particular technique known as tyrethermography. In this technique, tyres to be compared are driven inrotation by friction against a drum rotating at a predetermined speed.Applicants have used a drum of 1700 mm diameter, rotated at a speedequivalent to 120 km/hour. Tyres are mounted to the recommended rim foroperation, inflated to a pressure approaching the operating pressure,and pressed against the drum with a load corresponding to about therated running load of the tyre, as provided by E.T.R.T.O. (European Tyreand Rim Technical Organization) regulations.

After a time lag varying between 30 and 60 minutes, depending on thetyre size, the carcass structure, the tread pattern, and the ambienttemperature, it appeared that the inner (overall) temperature of thetyre reached a stable value. At that time the tread wasthermographically photographed using infrared light. The thermographyphotographs can be carried out both with the tyre at a standstill andwith the tyre in rotation, the modality being selected by theexperimenter depending on the specific requirements. The result ineither case is an image of the tyre tread that can be convenientlyreproduced in colours or on a grey-scale, in which the different coloursor grey shades identify, spot by spot, the different tread temperatures,both on the surface of the tread and at the bottom of the tread grooves.

FIG. 6 is a colour thermograph of a prototype tyre tread compared with atyre tread of conventional production manufactured by Pirelli. Theconventional tyre is quite similar to the prototype tyre, apart from thefact that the conventional tyre tread band is completely made of a blackblend.

On the chromatic scale selected by the Applicants, colour changes fromblue to red, passing by sky-blue, green, and yellow, as the temperatureincreases from 25° C. to 65° C. The photographed tyres are the tyreaccording to the invention, shown in FIG. 6 b, provided with ablack/white two-blend band having the white portion to the right, andthe Pirelli tyre “P 200 CHRONO ENERGY” of normal production, shown inFIG. 6 a.

The tested tyres had size 175/70R 13, were mounted to a rim type J 5.5″, inflated to a pressure of 2.2 bars, and submitted to a load of 450kg.

The compound blends of the two portions used in the tire according tothe invention had compositions set forth in the following Table 1:

TABLE 1 Ingredient Black Blend White Blend SBR 1712 80 SBR 1500 20OE-SSBR 80 BR 33 Carbon Black - N 220 45 Silica - VN3 available 20 70from DEGUSSA Binding Agent 1.6 5.6 ZnO 2.5 2.5 Stearic Acid 2 2Antioxidants 1.5 1.5 Anti-fatigue Agents 1 1 Plasticizers 10 5 Sulphur 11.4 Accelerating Agents 2.3 3.8

From FIG. 6 one can easily see that in the tyre made according to theinvention the colder sky-blue portion indicating 35° C. occupies aremarkably greater area than that of the reference tyre, where thewarmer green portion indicating 45° C. is prevalent. The colder areaalso extends further towards the left tyre shoulder made of black blendin the two-blend tyre, when compared to the corresponding portion of thereference tyre.

Measurements of the inner (overall) temperature of the tyre have given avalue of 53° C. for the tyre according to the invention, as compared toa value of 58° C. for the reference tyre.

Results achieved from different comparative road tests carried out withthe above tyres are reproduced in the following Table 2. Moreparticularly, column 1 of Table 2 refers to the test results achievedwith tyre “P 200 CHRONO ENERGY,” and column 2 of the Table refers toresults of a tyre according to the invention. Both tyres were mounted ona VOLKSWAGON POLO 1.4 car. Said Table 2 reproduces the results achievedin performance tests on a mixed route including one portion on a normalroad and one portion on a car track, on a dry road surface, at anambient temperature of 14° C.

TABLE 2 Tyres Performance 1 2 Running on a straight run Directionalstability 6.5 6.5 Steering rigidity 6.5 6.5 Fast run Empty on the centre6.0 6.5 Steering response speed 6.5 7.0 Steering response progressivity5.5 6.0 Directional stability on a bend 6.5 6.5 Realignment 5.5 6.5Extreme Conditions Yield 7.0 7.0 Release on bends 6.5 7.0Controllability 7.0 7.0

The assigned points indicate the score obtained by the correspondingtyres, on a 1 to 10 scale, based on the test driver's judgment, withreference to the different tyre qualities taken into account in thetest. The greater scores indicate better performance.

As one can see from Table 2, the qualities of the tyre according to theinvention are substantially identical to those of the conventional tyreunder normal operating conditions on a straight run, when the treadblend is not particularly under stress. On the contrary, the tyreaccording to the invention performs much better with increasedemployment severity and increasingly stressful conditions to which thetread blend is submitted. Particularly, when the heat generated in thetyre increased so that the temperature reached by the tread increased,the performance of the tyre according to the invention also improved,especially with respect to traction. Actually, from Table 2 one can notethat the tyre according to the invention has obtained a score higherthan that of the reference tyre from every point of view.

It is therefore apparent that the present invention has enabled thedesired improvements to be achieved by a synergetic combination betweendistinct tread band portions, made of a black (hot) blend and a white(cold) blend respectively, so that an exclusively positive overallresult is obtained, that is equal to or better than the results obtainedby conventional tyres, seen from any measure of tyre performance on aroad.

It is also clear that the invention has provided a convenient method ofreducing the operating temperature of the tyres while simultaneouslysafeguarding all required performance qualities. In particular, it isstill more evident how the invention can achieve excellent results withreference to recapped tyres, where adhesion between the alreadyvulcanized old carcass and the new, raw, or pre-molded tread band hasalways represented a particularly critical element due to itssensitivity to the operating temperature of the tyre, as proved by theseparated tread pieces that can be found on motorways.

Finally, it is apparent that the present invention description only hasan explanatory function and not a limiting function, so that a personskilled in the art, after understanding the invention as above describedwill be able to carry out modifications, variations, and replacements ofall variables associated with the present invention in order to meetparticular and contingent application requirements, depending on needs.

1-25. (canceled)
 26. A tyre for a wheel of a vehicle, comprising: atoroidal carcass provided with axially opposite sidewalls and beads foranchoring the tyre to a rim of the wheel; a tread band disposedcrownwise on the carcass, comprising a surface with a plurality ofhollows and grooves defining a raised tread pattern; and a beltstructure interposed between the carcass and the tread band, axiallyextending between the sidewalls; wherein the tread band comprises atleast first and second circumferential axially-contiguous portions,wherein the first portion is formed of a first composition comprising areinforcing filler having at least 40%-by-weight carbon black and atleast some white filler, wherein the second portion is formed of asecond composition comprising a reinforcing filler having at least20%-by-weight white filler, wherein a volume of the second portion doesnot exceed 80% of a combined volume of the tread band, wherein a firsthysteresis value of the first composition is different from a secondhysteresis value of the second composition, and wherein the differencebetween the first and second hysteresis values achieves a decrease in anoverall working temperature of the tyre relative to an otherwiseidentical tyre provided with a tread band made entirely of a compositionhaving the higher hysteresis value.
 27. A tyre for a wheel of a vehicle,comprising: a toroidal carcass provided with axially opposite sidewallsand beads for anchoring the tyre to a rim of the wheel; a tread banddisposed crownwise on the carcass, comprising a surface with a pluralityof hollows and grooves defining a raised tread pattern; and a beltstructure interposed between the carcass and the tread band, axiallyextending between the sidewalls; wherein the tread band comprises atleast first and second circumferential axially-contiguous portions,wherein the first portion is formed of a first composition comprising areinforcing filler having at least 40%-by-weight carbon black and atleast some white filler, wherein the second portion is formed of asecond composition comprising a reinforcing filler having at least20%-by-weight white filler, wherein a volume of the second portion doesnot exceed 80% of a combined volume of the tread band, wherein a firsthysteresis value of the first composition is different from a secondhysteresis value of the second composition, wherein the secondcomposition further comprises an amount of white filler greater than anamount of white filler in the first composition, wherein a differencebetween the two amounts of white filler is at least equal to 20% of theamount of white filler in the second composition, wherein the at leastfirst and second portions are arranged to contact a road surface, andwherein the difference between the first and second hysteresis valuesachieves a decrease in an overall working temperature of the tyrerelative to an otherwise identical tyre provided with a tread band madeentirely of a composition having the higher hysteresis value.
 28. Thetyre of claim 27, wherein a volume of the portion comprising the secondcomposition is at least 30% of a combined volume of the tread band. 29.(canceled)
 30. The tyre of claim 27, wherein a width of the portioncomprising the second composition is at least 25% of a combined width ofthe tread band.
 31. The tyre of claim 27, wherein a width of the portioncomprising the second composition does not exceed 80% of a combinedwidth of the tread band.
 32. The tyre of claim 27, wherein a width ofthe portion comprising the second composition is at least 50% of acombined width of the tread band.
 33. The tyre of claim 27, wherein thewhite filler is a silica-based reinforcing filler.
 34. The tyre of claim27, wherein the reinforcing filler of the portion comprising the secondcomposition is substantially free of carbon black.
 35. The tyre of claim34, wherein the reinforcing filler of the portion comprising the secondcomposition further comprises colored pigments.
 36. The tyre of claim27, wherein the portion comprising the second composition is located ina central area of the tread band.
 37. The tyre of claim 36, wherein theraised tread pattern is a symmetric tread pattern.
 38. The tyre of claim36, wherein the raised tread pattern is a directional tread pattern. 39.The tyre of claim 36, wherein the tread band has a ratio of curvature ofat least 0.15:1; wherein the ratio of curvature is a first distancedivided by a second distance, wherein the first distance is measuredalong an equatorial plane of the tyre from a line passing through afirst tread end and a second tread end to a tread center, and whereinthe second distance is measured along the line passing through the firsttread end and the second tread end, from the first tread end to thesecond tread end.
 40. The tyre of claim 27, wherein the portioncomprising the second composition is located adjacent to an edge of thetread band.
 41. The tyre of claim 40, wherein the raised tread patternis an asymmetric tread pattern having two axially distinctcircumferential areas, comprising: an inner area adapted for mountingtowards a centerline of the vehicle, and an outer area adapted formounting away from the centerline of the vehicle.
 42. A tread band forrecapping used tyres, comprising: at least first and secondcircumferential and axially-contiguous portions: wherein the firstportion is formed of a first composition comprising a reinforcing fillerhaving at least 40%-by-weight carbon black and at least some whitefiller, wherein the second portion is formed of a second compositioncomprising a reinforcing filler having at least 20%-by-weight whitefiller, wherein a volume of the second portion does not exceed 80% of acombined volume of the tread band, wherein a first hysteresis value ofthe first composition is different from a second hysteresis value of thesecond composition, wherein the second composition further comprises anamount of white filler greater than an amount of white filler in thefirst composition, wherein a difference between the two amounts of whitefiller is at least equal to 20% of the amount of white filler in thesecond composition, wherein the at least first and second portions arearranged to contact a road surface, and wherein the difference betweenthe first and second hysteresis values achieves a decrease in an overallworking temperature of the tyre relative to an otherwise identical tyreprovided with a tread band made entirely of a composition having thehigher hysteresis value. 43-46. (canceled)
 47. A method of reducing theoperating temperature of a tyre on a vehicle, comprising: forming atoroidal carcass provided with axially opposite sidewalls and beads foranchoring to a corresponding rim; forming a belt structure located onthe carcass, axially extending between the sidewalls; selecting a firstcomposition comprising a reinforcing filler having at least40%-by-weight carbon black and at least some white filler; selecting asecond composition comprising a reinforcing filler having at least20%-by-weight white filler; forming a tread band comprising at leastfirst and second circumferential and axially-contiguous portions; andforming a tyre comprising the carcass, the belt structure, and the treadband; wherein the first portion is made of the first composition,wherein the second portion is made of the second composition, wherein avolume of the second portion does not exceed 80% of a combined volume ofthe tread band wherein a first hysteresis value of the first compositionis different from a second hysteresis value of the second composition,wherein the second composition further comprises an amount of whitefiller greater than an amount of white filler in the first composition,wherein a difference between the two amounts of white filler is at leastequal to 20% of the amount of white filler in the second composition,wherein the at least first and second portions are arranged to contact aroad surface, and wherein the difference between the first and secondhysteresis values achieves a decrease in an overall working temperatureof the tyre relative to an otherwise identical tyre provided with atread band made entirely of a composition having the higher hysteresisvalue.
 48. A tyre for a wheel of a vehicle, comprising: a toroidalcarcass provided with axially opposite sidewalls and beads for anchoringthe tyre to a rim of the wheel; a tread band disposed crownwise on thecarcass, comprising a surface with a plurality of hollows and groovesdefining a raised tread pattern; and a belt structure interposed betweenthe carcass and the tread band, axially extending between the sidewalls;wherein the tread band comprises at least first and secondcircumferential and axially-contiguous portions, wherein the firstportion is formed of a first composition comprising a reinforcing fillerhaving at least 40%-by-weight carbon black and at least some whitefiller, wherein the second portion is formed of a second compositioncomprising a reinforcing filler having at least 20%-by-weight whitefiller, wherein a first hysteresis value of the first composition isdifferent from a second hysteresis value of the second composition,wherein the second composition further comprises an amount of whitefiller greater than an amount of white filler in the first composition,wherein a difference between the two amounts of white filler is at leastequal to 20% of the amount of white filler in the second composition,wherein a volume of the second portion is at least 30% of a combinedvolume of the tread band portions, wherein a volume of the secondportion does not exceed 80% of a combined volume of the tread band,wherein the at least first and second portions are arranged to contact aroad surface, and wherein the difference between the first and secondhysteresis values achieves a decrease in an overall working temperatureof the tyre relative to an otherwise identical tyre provided with atread band made entirely of a composition having the higher hysteresisvalue.
 49. A tyre for a motorcycle wheel, comprising: a toroidal carcassprovided with axially opposite sidewalls and beads for anchoring thetyre to a rim of the wheel; a tread band disposed crownwise on thecarcass, comprising a surface with a plurality of hollows and groovesdefining a raised tread pattern; and a belt structure interposed betweenthe carcass and the tread band, axially extending between the sidewalls;wherein the belt structure comprises a reinforcing wrapping of metallicinextensible cord disposed circumferentially to the carcass to form aplurality of turns parallel to each other and located consecutively in aside-by-side relationship, substantially oriented along a rollingdirection of the tyre, wherein the tread band comprises at least first,second, and third circumferential and axially-contiguous portions,wherein the first portion is formed of a first composition comprising areinforcing filler having at least 40%-by-weight carbon black and atleast some white filler, wherein the second portion is formed of asecond composition comprising a reinforcing filler having at least20%-by-weight white filler, wherein the third portion is formed of athird composition comprising a reinforcing filler having at least40%-by-weight carbon black and at least some white filler, wherein avolume of the second portion does not exceed 80% of a combined volume ofthe tread band, wherein a second hysteresis value of the secondcomposition is different from a first hysteresis value of the firstcomposition and a third hysteresis value of the third composition,wherein the second composition further comprises an amount of whitefiller greater than an amount of white filler in the first composition,wherein a difference between the amount of white filler in the first andsecond compositions is at least equal to 20% of the amount of whitefiller in the second composition, wherein the second composition furthercomprises an amount of white filler greater than the amount of whitefiller in the third composition, wherein a difference between the amountof white filler in the second and third compositions is at least equalto 20% of the amount of white filler in the second composition, whereinthe first portion is located on a first side of an equatorial plane ofthe tyre and the third portion is located on a second side of theequatorial plane of the tyre wherein the at least first, second, andthird portions are arranged to contact a road surface, and wherein adifference between the first, second, and third hysteresis valuesachieves a decrease in an overall working temperature of the tyrerelative to an otherwise identical tyre provided with a tread band madeentirely of a composition having the highest hysteresis value.